Dissident republicans have limited support and have no chance of achieving their aims, Deputy First Minister Martin McGuinness has said.

He urged people to stand firm after the Real IRA threatened to "execute" police officers, branded the Queen's visit to the Irish Republic an insult and denounced the GAA, Catholic Church and constitutional nationalism.

A statement from the terrorist group was read by a masked man in a Londonderry cemetery at a rally organised by the 32 County Sovereignty Movement to mark the anniversary of the 1916 Easter Rising.

Irish deputy prime minister Eamon Gilmore also joined Mr McGuinness in claiming the dissidents had no mandate.

Mr McGuinness said: "It's quite clear from the comments that were made yesterday that they see Sinn Fein and all of the other political parties on this island, the Catholic Church and the GAA and indeed the Protestant churches, they see all of us as the enemy," Mr McGuinness said.

"I suppose it begs the question, given that they would say that they're committed to Irish reunification, how do you bring about Irish unity without the support of the people of Ireland?

"That's the big question that they need to answer."

Mr McGuinness said dissident republicans had three aims - to destroy the peace process, break up his relationship with First Minister Peter Robinson and turn back the tide on policing.

"I think what we have to do is we have to be moving forward very confident about the future, because the unity that has been seen by all of the elected representatives on the island of Ireland, supported by the entire community, sends a very clear message to these people that there's no prospect whatsoever of them achieving any of the objectives that they've set themselves," he told RTE radio.

The Real IRA statement came as security forces faced a heightened threat after the recent murder of Catholic constable Ronan Kerr, 25, in a booby-trap bomb under his car in Omagh, Co Tyrone.